1. Field of the Invention
This invention relates to semiconductor device fabrication and, in particular, to semiconductor device fabrication involving plasma processing.
2. Art Background
During the fabrication of devices, typically a substrate is subjected to processing. For example, the substrate is subjected to a species generated in a plasma to induce removal of portions of the substrate surface layer. (In the context of this invention a substrate is a body being processed into optical or electronic device(s), e.g. semiconductor devices that includes regions of semiconductor material, dielectric material, and/or conductive material.) Alternatively, a plasma is employed to induce removal or deposition of material on a substrate through interaction of species generated in the plasma or through interaction between plasma generated species and a predominantly non-ionized gas.
Monitoring of the gas phase and surface processes are essential to device fabrication. In etch procedures, it is extremely important to determine when one material region has been removed to terminate the etch before destruction of underlying regions occurs. Similarly, in deposition procedures it is desirable to monitor the quality of the material being deposited.
A number of procedures are available at least for etch monitoring. For example, in an etching process the substrate is subjected to coherent radiation. Interference patterns generated by interaction of light reflected by the substrate upper surface and an interior substrate layer interface yield a measure of the time-dependent thickness of the region being etched. Alternatively, spontaneous or fluorescent emission induced by subjecting the plasma to coherent radiation is indicative of the material being etched from the substrate. When the fluorescence wavelength or intensity changes, a compositional change of the material being etched is signaled. If the uncovered material is not to be etched, the plasma procedure is then terminated.
Most plasma monitoring techniques rely on the optical detection of a signal induced by incident electromagnetic radiation. Although optical monitoring of plasma processes has proven to be extremely valuable, some improvement is still desirable. For some procedures, interference between light generated by the plasma and the optical signal presents detection difficulties. Optical techniques generally give no information about the surface composition. Optical procedures also generally require an optical path for incoming radiation and a second path for the signal being detected. This dual optical access is not always entirely convenient. Additionally, it is desirable to enhance detection sensitivity to the surface composition of the wafer.